Have you already solved the problem?
I will present my solution for anyone who comes across this article in the future.
I am not a native English speaker so I am using translation software.
I have the same symptom, and I have been investigating for a while now, but I solved it by accident.
As it turns out, I imported a character that was already prepared in MetaHuman via Bridge without any editing at all. For some reason, even my own character’s eyelashes, which were problematic, were cured. (In my case, I imported Hana because my character was a female character.)
I have no idea why it was fixed, but I suspect that something in the Common file was at work.
I don’t know if your problem is solved in the same way, but please give it a try.